This study will determine whether a continuous 24h infusion of MK-751 (a GHRP-mimetic) will result in increased or attenuated GH secretion and whether GH response to an IV dose of GHRH at the end of the infusion will be enhanced. Prolactin and cortisol will also be measured to determine specificity of action of MK-751 when chronically administered. Study completed and published. Six older adults (4 men, 2 women) received 12 h and 24 h iv infusions of a GHRP mimetic (L-692,429, developed by Merck Laboratories). Pulsatile GH secretion was enhanced (by increasing the mass of GH secreted but not number of secretory pulses), with a compensatory hyposecretion after cessation of the infusion. GH response to GHRH was also enhanced.